Motion & Colour Perception Flashcards
(41 cards)
1
Q
What are the functions of motion perception? (6)
A
- Break camouflage
- Attract attention
- Segregate objects from background
- Interpret events
- Determine structure of objects
- Determine what actions people are performing
2
Q
Describe breaking camouflage
Motion Perception
A
- Something camouflaged can be virtually invisible
- Until it moves
- Attention attracted
- Segregated from background
- Until it moves
3
Q
Describe attracting attention
Motion Perception
A
- Something moves
- Attention is attracted to it
4
Q
Describe interpreting events
Motion Perception
A
- Seeing how objects interact
-
Infer causality and social relationships
- From only movements can infer what talking subject is
-
Infer causality and social relationships
5
Q
Describe infering structure
Motion Perception
A
- Kinetic Depth Effect
- Motion helps in determining the shape of a moving object
6
Q
Describe interpreting actions
Motion Perception
A
-
Ambiguous static pose
- Add motion = Actions and intentions made clear
- Demonstrated using point-light walkers
7
Q
What are point-light walkers?
Motion Perception
A
- Lights placed on a person’s joints
- Have them perform an action
- Recorded so that only light can be seen
- Can determine what action was performed from video
8
Q
What is akinetopsia?
A
-
No longer able to perceive motion
-
Damage to brain responsible for motion perception
- Medial temporal area
-
Damage to brain responsible for motion perception
9
Q
Describe the case of LM
A
- Akinetopsia
- Difficulties with…
- Pouring a cup of tea
- Crossing the street
- Following speech
-
Could see that things had moved
- Couldn’t see them moving
10
Q
When do we perceive motion?
A
- Real Motion → Actual movement
-
Illusory motion → Not actual movement
- Apparent motion
- Static image (illusions)
-
Motion aftereffects
- Abundance of motion → Stationary scene = Stationary scene going backwards
- Induced Motion → Moving background = Stationary object appears to move
11
Q
Describe apparent motion
A
- Series of stationary images presented in succession
- Gives impression of motion
- Dots sufficiently close together
- Can’t be too far apart
- Alternation rate can’t be too fast
- As separation increases alternation rate tends to decrease
-
Insensitive to colour changes
- If ambiguous motion then colour can disambiguate
Korte’s Third Law of Apparent Motion
12
Q
Describe motion aftereffects
A
-
Looking at something moving for a while
-
Motion receptors habituated
- Excite motion receptors for one direction
- Neurons exhausted
-
Motion receptors habituated
- Looking at something stationary
-
Seems to move backward
- Complementary neurons that are usually inhibited (by the other direction) are excited (up/down)
-
Seems to move backward
13
Q
What is induced motion?
A
- Nearby object (usually large) affects perceived motion of second object (usually small)
- Or causes a second object to appear to move
14
Q
What is motion induced blindness?
A
- Motion causing things to disappear
15
Q
Describe the motion induced blindness demo of Bonneh et al. (2001)
A
- Green flashing spot (fixation)
- Multiple rotating blue crosses
- Cause 3 yellow dots to disappear
16
Q
What is motion induced change blindness?
A
- Harder to notice changes because of motion
17
Q
Describe the motion induced change blindness demo of Suchow & Alvarez (2011)
A
- (When stationary) Colour changes attract attention because of transient signals associated with the change
- Movement → Transient signals with all objects (not just ones changing)
- Attention no longer drawn preferentially to changing objects
- Changes not noticed
18
Q
Describe motion illusions (footsteps illusion)
A
- Inform us of the processes underlying motion perception
- Higher contrast = Faster
- Lower contrast = More slowly
-
Footsteps Illusion
- Rectangles have opposing contrasts while at same horizontal position
- Meaning that they appear to speed up and slow down at different times
19
Q
What is the aperture problem?
Motion Illusion
A
-
Can’t see ends of line → Movement is ambiguous
- Motion of line through aperture (opening) is “captured” by movements of terminators
- Points where line joins aperture
- Motion of line through aperture (opening) is “captured” by movements of terminators
-
Motion of terminators determines perceived motion of line
- Vertical = Vertical, Horizontal = Horizontal
- If actual ends of line visible = See actual motion
20
Q
What is the function of colour perception?
A
- Suggested that colour vision evolved primarily to help humans search for things
-
Making judgements
- Ripeness of fruits
- Poisonous animals are often coloured
- Finding mates
21
Q
Describe the physics of colour
A
- Visible light is electromagnetic radiation with wavelengths varying about 400nm to about 700nm
- 400nm = Blue
- 700nm = Red
- White light is a mixture of all wavelength
22
Q
Describe the colour of opaque objects
A
- Opaque objects → Objects that light cannot pass through
- Not at all transparent
- Colour determined by the light that it reflects
- Examples
- Absorbs blue light but reflects red light = Looks red
- Reflects all light = Looks white
23
Q
Describe the colour of transparent objects
A
-
Colour determined by the colour it transmits
- Absorbs blue but transmits red = Looks red
24
Q
Describe mixing (blue and yellow) paint
A
- What paint absorbs
- Blue + Yellow
- Blue absorbs red but reflects blue and green
- Yellow absorbs blue but reflects red and green
- Mixing creates a mixture that absorbed red and blue but reflects green
- Looks green
25
Describe mixing light
* Additive
* Red + green = Yellow
* **Blue + yellow (R+G) = White**
* Contained blue, green and red
* White light is a mixture of the three colours
26
What is the Munsell Colour System?
* Colours categorised according to...
* **Value (lightness)**
* **Hue (colour)**
* **Chroma (saturation)**
27
What is the trichromatic theory of vision?
* Retina has photoreceptors known as...
* Rods
* Cones
28
Describe rods
## Footnote
Trichromatic Theory of Vision
* **Cannot distinguish between colours** and are **active only at low light levels**
* Normal light = Inactive (only cones active) → Because highly sensitive
* Use up all neurotransmitter + action potential in low light = Exhausted in normal light
29
Describe cones
## Footnote
Trichromatic Theory of Vision
* Three types that response maximally to a different wavelength
* **S cones - 419nm (blue)**
* **M cones - 531nm (mainly green)**
* **L cones - 558nm (mainly red)**
* Comparing relative activities = Distinguish colours
* Don't work in dark light
## Footnote
**C**ones = **C**olour
30
Distinguish between when rods and cones are active
* **No colour → Have switched to rods**
* **Can't see details when looking directly**
* Looking directly = **Centre of retina** (fovea)
* Fovea has **dense photoreceptors that give highest detail**
* They are **cones (which don't work in low light)**
* At night fixating = Putting it on part with *no rods*
* Therefore need to look **slightly off something** you want to see (not direct = use rods)
31
Distinguishing between colours
* Compare relative activities of cones
* Depending on which are most active
32
Describe colour matching
* **Adjusting amount of B, G and R light we can match the cone activations**
* Even though light patches are different
33
What are metamers?
* **Physically different stimuli** that **appear the same**
34
Describe monochromatism
* No functioning cones
* **Only functioning rods**
* See world only in **shades of gray**
* **Very sensitive to light**
* Need to wear dark glasses during the day
* Need to make everyday light same as darker conditions as rods are sensitive
35
Describe the types of dichromats
* Can't distinguish, can distinguish
* **Protanopes**
* **No L cone** - **See blue and yellow**
* ✖️ - Red and Green
* ✔️ - Blue and Green, Blue and Red
* 420 and 560nm
* **Deuteranopes**
* **No M cone** - **See blue and yellow**
* ✖️ - Red and Green
* ✔️ - Blue and Green, Blue and Red
* 420 and 640nm
* **Tritanopes**
* **No S cone** - **See blue and red**
* ✖️ - Blue and Green
* ✔️ - Blue and red, Red and green
* 560 and 640nm
36
What are unilateral dichromats?
* **Normal trichromatic vision in one eye but dichromatic vision in the other eye**
* Help with **insight into dichromats**
* Protanopes and deuteranopes = See **blue and yellowish-green**
* Tritanopes = **See blue and red**
37
What is the opponent-process theory of colour vision?
* **Colour we perceive is determined not only by cones**
* **Signals** from cones are **processed by cortex where they are combined into 3 colour opponent channels**
* **Red-green**
* **Blue-yellow**
* **White-black**
* Evidence
* Afterimages
* Impossible colours
38
Describe afterimages
## Footnote
Psychophysical evidence for Opponent-Process Theory of Colour Vision
* **Viewing red stimulus - L cones more stimulated than M**
* Red percept activated more than **green (suppressed)**
* Therefore **see red**
* ***L cones habituate and become less sensitive to stimulus***
* **White shown = Green stronger than red**
* *L cones are exhausted*
* Get **green afterimage because M cones not exhausted**
* Same for blue and yellow
39
Describe impossible colours
## Footnote
Psychophysical evidence for Opponent-Process Theory of Colour Vision
* Some colour combinations are impossible
* ✔️- Bluish red (purple), yellowish red (orange), yellowish green
* ✖️ - **Can't perceive bluish yellow or reddish green**
* Blue + yellow light = White
* Blue and yellow are opponent colours
* Red + green light = Yellow
* Red and green are opponent colours
40
What is colour constancy?
* **Colour of light an object reflects is determined not only be reflectance**
* Also by colour of **light shining on it**
* White = Reflects colour of object
* **But enough of any other colour = Object reflects that colour because that is the only colour available**
* Light reflected determined by...
* **Reflectance x Illumination = Reflected light**
41
How does the visual system achieve colour constancy?
* **Habituating** to the colour
* Becoming **less sensitive**
* Entire scene under **red light = Everything looks greener than it actually is**
* We **discount the illuminant**
* When ***habituation cannot occur*** - Realising that **background is predominantly one colour**
* Tile in two photos is **reflecting the same light (gray) but in one photo looks blue and the other looks yellow**
* Able to *determine actual colour*
